Thin plate burring processing method and thin plate female screw-forming method

ABSTRACT

A thin plate burring processing method includes a first step of forming a thin portion thinner than an original thickness in a target portion by performing crushing processing on the target portion of a plate-like workpiece, a second step of forming a circular through-hole in the thin portion by punching processing, and a third step of forming an annular portion rising from a surface of the workpiece by performing projection processing with burring processing around the through-hole formed in the thin portion.

PRIORITY CLAIM

The present application is based on and claims priority from Japanese Patent Application No. 2011-276577, filed on Dec. 19, 2011, the disclosure of which is hereby incorporated by reference in its entirety.

BACKGROUND

1. Field of the Invention

The present invention relates to a thin plate burring processing method which forms a cylindrical rising portion in a thin plate by burring processing and a thin plate female screw-forming method which forms a female screw in an inside wall surface of the rising portion.

2. Description of the Related Art

It is known that burring processing is performed on a screw-fastening portion of a workpiece to form in the screw-fastening portion an annular portion projecting outward from the surface of the workpiece, and to form a female screw in the inside wall surface of the annular portion when fastening parts or the like to a metal plate-like workpiece or fastening the workpiece to a structure or the like by means of a screw.

As a conventional technique, it is described in, for example, JP H08-257646A that a circular through-hole is previously formed in a target portion of a workpiece by punching processing before performing burring processing, and an annular portion rising from the surface of the workpiece is formed by expanding the peripheral wall of the through-hole by performing the burring processing around the through-hole.

As a conventional technique, it is also proposed in, for example, JP 2004-223583A that a target portion of a workpiece is formed into a convex shape by performing drawing processing on the target portion, a through-hole is formed in the center of the convex shape by punching processing, and then burring processing is performed.

However, the poor strength of the screw-fastening portion is a problem in JP H08-257646A. Namely, in recent years, it has been required to reduce the thickness of a plate-like metal workpiece to lower manufacturing costs by cutting down on the used amount of a material. If the thickness of the workpiece is reduced, the projection amount of the annular portion is reduced. If the projection amount is reduced, the length of the screw-fastening portion is reduced, so that screw fastening can not be performed by a desired fastening torque.

The fastening torque can be increased in the screw-fastening operation in a production line. However, screw breakdown easily occurs if the fastening torque is increased in a state in which the length of the screw-fastening portion is short.

The conventional technique described in JP 2004-223583A is not economical because a thick convex portion is obtained by simply forming the convex portion with the drawing processing, the through-hole is formed in the thick convex portion by the punching processing, and the punched circular plate-like member is disposed of as scrap. If the portion to be disposed of as the scrap is left in the workpiece, it becomes a part of the annular portion in the burring processing, and it contributes to an increase in the projection amount of the annular portion.

SUMMARY

It is, therefore, an object of the present invention to provide a thin plate burring processing method capable of increasing the projection amount of an annular portion by burring processing even if a thin plate workpiece is used, and also a thin plate female screw-forming method which forms a female screw in an inside wall surface of a rising portion.

To attain the above object, one embodiment of the present invention provides a thin plate burring processing method, including: a first step of forming a thin portion thinner than an original thickness in a target portion by performing crushing processing on the target portion of a plate-like workpiece; a second step of forming a circular through-hole in the thin portion by punching processing; and a third step of forming an annular portion rising from a surface of the workpiece by performing projection processing with burring processing around the through-hole formed in the thin portion.

One embodiment of the present invention also provides a thin plate female screw-forming method, including: a first step of forming a thin portion thinner than an original thickness in a target portion by performing crushing processing on the target position of a plate-like workpiece; a second step of forming a circular through-hole in the thin portion by punching processing; a third step of forming an annular portion rising from a surface of the workpiece by performing projection processing with burring processing around the through-hole formed in the thin portion; and a fourth step of forming a female screw in an inside wall surface of the annular portion.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the specification, serve to explain the principle of the invention.

FIG. 1 is a view describing a thin plate burring processing method according to Embodiment 1 of the present invention.

FIG. 2A is a view illustrating the thin plate burring processing method according to Embodiment 1.

FIG. 2B is a view illustrating a conventional thin plate burring processing method.

FIGS. 3A, 3B are views each illustrating a part of the thin plate burring processing method according to Embodiment 1. FIG. 3A is a view illustrating an area where a surface of a plate-like member is formed into a convex shape or a concave shape, and FIG. 3B is a view illustrating an area inside an outer diameter of an annular portion formed by the burring processing.

FIG. 4A, 4B, 4C are views each illustrating a part of the thin plate burring processing method according to Embodiment 1. FIG. 4A is a view illustrating a state in which a lower surface side of a workpiece is formed into a convex shape to form a thick portion, FIG. 4B is a view illustrating a state in which an upper surface side of the workpiece is formed into a convex shape to form a thick portion, and FIG. 4C is a view illustrating a state in which the upper surface side and the lower surface side of the workpiece are formed into a convex shape to form a thick portion.

FIGS. 5A, 5B are views each illustrating a conventional example. FIG. 5A is a view illustrating a state in which a thin portion is formed by drawing processing, and FIG. 5B is a view illustrating a state in which a thin portion is formed in an annular portion by burring processing.

FIGS. 6A, 6B are views each illustrating a part of the thin plate burring processing method according to Embodiment 1. FIG. 6A is a view illustrating a thin area obtained by crushing processing and FIG. 6B is a view illustrating an area where a circular through-hole is punched by punching processing.

FIG. 7A, 7B are views each illustrating Embodiment 2. FIG. 7A is a view illustrating a state in which a female screw is formed in an inside wall surface of an annular portion and FIG. 7B is a view illustrating a state in which a workpiece is fastened to another member by a screw.

FIG. 8 is a view illustrating an evaluation result of breakdown torque value of a female screw in Embodiment 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

Embodiment Embodiment 1

FIG. 1 is a view illustrating a thin plate burring processing method according to Embodiment 1. The thin plate burring processing method includes a first step which forms a thin portion thinner than an original thickness in a target portion by performing crushing processing on the target portion of a plate-like workpiece, a second step which forms a circular through-hole in the thin portion by punching processing, and a third step which forms an annular portion rising from the surface of the workpiece by performing projection processing with burring processing around the through-hole formed in the thin portion.

The thin plate burring processing method according to the present embodiment will be described in detail.

According to the thin plate burring processing method of the present embodiment, as illustrated in FIG. 1, a plate-like workpiece 11 is prepared, and this workpiece 11 is placed on a lower die 12. In this case, an upper die 13 is provided above the workpiece 11. The lower die 12 and the upper die 13 are used for crushing processing. The lower die 12 includes an inverted truncated cone concave portion 12A having a narrow depth and the upper die 13 includes an inverted truncated cone projection 13A projecting downward.

By lowering the upper die 13, the crushing processing is performed on the target portion of the workpiece 11. An inverted truncated cone concave portion 11A is thereby formed on the upper surface side of the workpiece 11, and an inverted truncated cone convex portion 11B projecting downward is thereby formed on the lower surface side of the workpiece 11. The central axis of the concave portion 11A conforms to the central axis of the convex portion 11B.

In the present embodiment, a bottom wall (the wall portion between the bottom surface of the concave portion 11A and the lower surface of the convex portion 11B) of the inverted truncated cone concave portion 11A is formed to be thinner by the crushing processing, so as to form a thin portion 11C having a thickness thinner than an original thickness t1 of the workpiece 11. The thickness of the thin portion 11C is t2 (t2<<t1).

Next, a lower die 14 and an upper die 15 for punching processing are prepared, and the workpiece 11 after being crushed is placed on the lower die 14. The lower die 14 includes a concave portion 14A corresponding to the concave portion 12A of the lower die 12 for the crushing processing. A circular hole 14B is provided in the center of the concave portion 14A. An annular projection 15A projecting downward is provided in the upper die 15. The thin portion 11C of the workpiece 11 is arranged to fit to the hole 14B of the lower die 14 and the projection 15A of the upper die 15.

Then, the punching processing is carried out on the workpiece 11 by lowering the upper die 15, and a circular through-hole 11D is formed in the bottom portion of the concave portion 11A. In this case, the thin portion 11C is cut by the punching processing, and a circular plate-like scrap 11C′ is produced. This scrap 11C′ is disposed of.

Finally, a lower die 16 and an upper die 17 for burring processing are prepared, and the workpiece 11 after the punching processing is placed on the lower die 16. The lower die 16 includes a circular hole 16A having a size according to the outer diameter of the convex portion 11B of the workpiece 11. The workpiece 11 is arranged such that the convex portion 11B fits the hole 16A of the lower die 16. The upper die 17 includes a cylindrical projection 17A projecting downward.

Then, projection processing with the burring processing is performed on the workpiece 11 by lowering the upper die 17, so as to increase the diameter of the concave portion 11A of the workpiece 11, so that an annular portion 11E rising from the surface of workpiece 11 is formed. In the figures, the annular portion 11E faces downward, but the annular portion 11E becomes a shape rising from the surface of the workpiece 11 by performing the burring processing upside down.

FIG. 2A is a view illustrating the thin plate burring processing method according to the present embodiment. FIG. 2B is a view illustrating a conventional thin plate burring processing method.

In the thin plate burring processing method of the present embodiment, as illustrated in FIG. 2A, the crushing processing is performed on the workpiece 11 to form the thin portion 11C in the bottom portion of the concave portion 11A. After that, the thin portion 11C is punched by the punching processing. Therefore, the thin plate burring processing method of the present embodiment has an effect which can reduce the amount of material to be disposed of as the scrap 11C′.

On the other hand, in the conventional thin plate burring processing method, as illustrated in FIG. 2B, the punching processing is performed on the workpiece 11 without performing the crushing processing or the like. Namely, the punching processing is directly performed on the target portion of the workpiece 11 by using a not shown die (lower and upper dies) so as to form a circular through-hole 11F in the workpiece 11. For this reason, the thickness of the scrap 11F′ is equal to the original thickness of the workpiece 11, and thus, the conventional thin plate burring processing method is not economical because the amount of material to be disposed of as a scrap 11F′ is large.

Moreover, the height of an annular portion 11G projecting downward from the surface of the workpiece 11 is small when performing the burring processing on the workpiece 11 because the amount of material to be disposed of as the scrap 11F′ is large.

In the present embodiment, the height of the annular portion 11E is higher than the height of the conventional annular portion 11G by h (=h1−h2), where the height of the annular portion 11E in the present embodiment is h1 and the height of the conventional annular portion 11G is h2 (<h1).

FIGS. 3A, 3B are views each illustrating a part of the thin plate burring processing method according to the present embodiment. FIG. 3A is a view illustrating an area where the surface of the workpiece 11 is formed into a convex shape or a concave shape. FIG. 3B is a view illustrating an area inside the outer diameter of the annular portion formed by the burring processing.

FIG. 3A illustrates the workpiece 11 after the crushing processing. In FIG. 3A, S1 illustrates an area where the surface of the workpiece 11 is formed into a concave shape or a convex shape. Namely, when the crushing processing is performed on the workpiece 11, the inverted truncated cone concave portion 11A is formed on the upper surface side of the workpiece 11 and the inverted truncated cone convex portion 11B is formed on the lower surface side of the workpiece 11 by the flow of the crushed material of the workpiece 11. In this case, S1 is an area between positions P1, P1, where the maximum diameter of the convex portion 11B is located. This area S1 includes a circular shape as seen in the workpiece 11 from below.

FIG. 3B illustrates the workpiece 11 after the burning processing. In FIG. 3B, S2 illustrates an area inside the outer diameter of the annular portion 11E formed by the burring processing.

In the present embodiment, the area S1 is previously set to be equal to or smaller than the area S2. Namely, the maximum diameter of the concave portion 12A of the lower die 12 for the crushing processing is set to be equal to or smaller than the inner diameter of the hole 16A of the lower die 16 for the burring processing.

With this configuration, the area where the surface of the workpiece 11 is formed into a concave shape and/or a convex shape by the flow of the material with the crushing processing is reduced to be smaller than, for example, the area inside the outer diameter of the annular portion 11E formed by the burring processing, so that the material of the annular portion 11E which projects by the burring processing is effectively used; thus, the height of the projection can be further increased.

FIGS. 4A, 4B, 4C are views each illustrating an example in which a thick portion thicker than the original thickness of the workpiece 11 is formed in the area where the surface of the workpiece 11 is formed into the concave shape and/or convex shape by the flow of the crushed material of the workpiece 11. FIG. 4A is a view illustrating the convex shape on the lower surface side of the workpiece 11. FIG. 4B is a view illustrating the convex shape on the upper surface side of the workpiece 11. FIG. 4C is a view illustrating the convex shape on the upper and lower surface sides of the workpiece 11.

In FIG. 4A, S3 is an area between a position P2 where the maximum diameter of the convex portion 11B is located and a position P3 where the maximum diameter of the concave portion 11A is located. The entire area S3 includes an annular shape.

In FIG. 4B, similar to FIG. 4A, the concave portion 11A is provided on the upper surface side of the workpiece 11, and the convex portion 11H is provided on the upper surface side of the workpiece 11. In FIG. 4B, an area S4 is provided between a position P4 where the maximum diameter of the convex portion 11H is located and a position P5 where the maximum diameter of the concave portion 11A is located. The entire area S4 includes an annular shape.

In FIG. 4C, a convex portion 11J and a concave portion 11K are provided on the upper surface side of the workpiece 11, and a convex portion 11L and a concave portion 11M are provided on the lower surface side of the workpiece 11. In FIG. 4C, an area S5 is provided between a position P6 where the maximum diameter of the convex portion 11J is located and a position P7 where the maximum diameter of the concave portion 11K is located, and between a position P8 where the maximum diameter of the convex portion 11L is located and a position P9 where the maximum diameter of the concave portion 11M is located. The entire area S5 includes an annular shape.

FIG. 5A, 5B illustrate a conventional example. FIG. 5A is a view illustrating a thin portion formed by drawing processing. FIG. 5B is a view illustrating a thin portion formed in an annular portion by burring processing.

As illustrated in FIG. 5A, if an inverted truncated cone convex portion 21 projecting downward is formed in the workpiece 11 by performing the drawing processing on the workpiece 11, the thickness of an inclined wall 21A of the convex portion 21 is approximately equal to the original thickness t1 of the workpiece 11 in the top portion, but the thickness is gradually reduced toward the bottom portion to be thinner than the original thickness t1.

If the burning processing is performed on the workpiece 11 in the state illustrated in FIG. 5A, it is general that the thickness of the annular portion 22 is gradually reduced from the bottom toward the leading end. If the thickness of the annular portion 22 is reduced, the fastening strength is reduced when the workpiece 11 is fastened to another plate or the like by using a female screw formed in the inner wall surface of the annular portion 22.

In the present embodiment, the crushing processing illustrated in FIGS. 4A, 4B, 4C is performed in advance on the workpiece 11, so that the annular portion includes a desired thickness from the bottom to a portion just before the leading end portion of the annular portion although the leading end portion of the annular portion includes a thin portion when the burning processing is performed. Then, by cutting the thin leading end portion, the annular portion 11E having a uniform thickness and high projection can be obtained. As a result, the fastening strength can be improved when the workpiece 11 is fastened to another plate or the like by using the female screw formed in the inner wall surface of the annular portion 11E.

FIGS. 6A, 6B are views each illustrating a part of the thin plate burring processing method according to the present embodiment. FIG. 6A is a view illustrating a thin area obtained by the crushing processing. FIG. 6B is a view illustrating an area in which a circular through-hole is punched by the punching processing.

The thin portion 11C is formed in the bottom portion of the inverted truncated cone concave portion 11A of the workpiece 11 by the crushing processing. This thin portion 11C is punched by the punching processing, so that the through-hole 11D and also the scrap 11C′ are formed.

In the present embodiment, a thin portion area S6 is set to be equal to or smaller than the area of the through-hole 11D formed by the punching processing.

With this configuration, the material to be eliminated as the scrap 11C′ is reduced, and the material for use in the annular portion 11E which is processed by the burring processing of the next step is increased, so that the height of the projection can be further increased.

Embodiment 2

Next, a thin plate female screw-forming method according to Embodiment 2 will be described. The thin plate female screw-forming method of the present embodiment includes a first step which forms a thin portion thinner than an original thickness in a target portion by performing crushing processing on a target portion of a workpiece, a second step which forms a circular through-hole in the thin portion by punching processing, a third step which forms an annular portion rising from the surface of the workpiece by performing projection processing with burning processing around the through-hole formed in the thin portion, and a fourth step which forms a female screw in an inside wall surface of the annular portion.

FIGS. 7A, 7B are views each illustrating Embodiment 2. FIG. 7A is a view illustrating a state in which a female screw is formed in the inside wall surface of the annular portion of the workpiece. FIG. 7B is a view illustrating a state in which the workpiece is fastened to another member by a screw.

As illustrated in FIG. 7A, a female screw 31 is formed in the inside wall surface of the annular portion 11E manufactured by the thin plate burring processing method of Embodiment 1.

Then, as illustrated in FIG. 7B, a plate 33 having a through-hole 32 is prepared, and a male screw 34 is inserted into the through-hole 32, and a screw portion 34A of the male screw 34 is fastened to the female screw 31 of the annular portion 11E. The workpiece 11 can be thereby strongly fastened to a plate 33.

According to the above configuration, the annular portion 11E having high projection can be obtained in a thin plate, and a strong fastening torque tolerance female screw can be achieved by using the inside wall surface of the annular portion 11E as the female screw

FIG. 8 is a graph illustrating an evaluation result of a breakdown torque value for the female screw according to the present embodiment. In FIG. 8, light hatching illustrates a case in which the female screw is formed in the annular portion manufactured by the conventional thin plate burring processing method, and thick hatching illustrates a case in which the female screw is formed in the annular portion manufactured by the thin plate burring processing method of the present embodiment.

More specifically, test target members #1, #2 were manufactured by the conventional thin plate burring processing method and test target members #1, #2 were manufactured by the thin plate burring processing method of the present embodiment. The size and the material of the test target members #1, #2 by the thin plate burring processing method of the present embodiment were the same as those of the conventional thin plate burring processing method.

As illustrated in FIG. 8, the female screw breakdown torque by the thin plate burring processing method of the present embodiment was larger than the female screw breakdown torque by the conventional thin plate burring processing method in both cases of the test target members #1, #2, and the effect of the thin plate female screw-forming method of the present embodiment could be confirmed.

According to the configurations described in the embodiments of the present invention, the thickness of the crushed portion by the crushing processing of the first step was reduced, and the punching processing of the second step was performed on the crushed portion, so that the amount (volume) of the circular scrap punched by the punching processing was very small. Namely, a part of the scrap conventionally disposed of in the technique was included in the annular portion by the burring processing. Therefore, the projection amount (the height of the rising portion) of the annular portion could be increased. Thus, a desired fastening torque could be easily obtained when fastening the workpiece by a screw.

According to the embodiments of the present invention, a thin plate burring processing method capable of increasing the projection amount of the annular portion by the burring processing even if the thickness of the workpiece is reduced can be provided.

Moreover, a thin plate female screw-forming method which forms a female screw in the inside wall surface of the rising portion of the annular portion can be provided.

Although the embodiments of the present invention have been described above, the present invention is not limited thereto. It should be appreciated that variations may be made in the embodiments described by persons skilled in the art without departing from the scope of the present invention. 

What is claimed is:
 1. A thin plate burring processing method, comprising: a first step of forming a thin portion thinner than an original thickness in a target portion by performing crushing processing on the target portion of a plate-like workpiece; a second step of forming a circular through-hole in the thin portion by punching processing; and a third step of forming an annular portion rising from a surface of the workpiece by performing projection processing with burring processing around the through-hole formed in the thin portion.
 2. The thin plate burring processing method according to claim 1, wherein an area where the surface of the workpiece is formed into a concave shape and/or a convex shape by flow of a crushed material of the workpiece is previously set to be equal to or smaller than an area inside an outer diameter of the annular portion formed by the burring processing.
 3. The thin plate burring processing method according to claim 1, wherein a thick portion thicker than the original thickness of the workpiece is formed in an area where the surface of the workpiece is formed into a concave shape and/or a convex shape by flow of a crushed material of the workpiece.
 4. The thin plate burring processing method according to claim 1, wherein an area of the thin portion formed by the crushing processing is previously set to be equal to or smaller than an area of the through-hole formed by the punching processing.
 5. A thin plate female screw-forming method, comprising: a first step of forming a thin portion thinner than an original thickness in a target portion by performing crushing processing on the target position of a plate-like workpiece; a second step of forming a circular through-hole in the thin portion by punching processing; a third step of forming an annular portion rising from a surface of the workpiece by performing projection processing with burring processing around the through-hole formed in the thin portion; and a fourth step of forming a female screw in an inside wall surface of the annular portion. 